22 EQUISETACE.E. 



Group PTERIDOPHYTA. 

 (VASCULAR CRYPTOGAMS.) 



Plants with a highly organized sporophyte generation, possessing 

 true vascular (conducting) tissue, and true roots. 



With the exception of Isoetes, Botrychium, Helminthostachys, 

 and, according to recent observations, Equisetum? there is no 

 secondary thickening in the vegetative structures of the living 

 genera included in this group. Among fossil genera secondary 

 thickening appears to have been common. 



The Pteridophyta differ from the Bryophyta in the greater advance 

 in physiological division of labour as expressed in the more com- 

 plete differentiation of tissues. The presence of a true vascular 

 system and the possession of true roots at once separate the 

 Pteridophyta from the next lower group of plants. In the 

 higher group the sporophyte generation is the more conspicuous; 

 in the Bryophyta the gametophyte (oophyte) generation is more 

 prominent. 



Class EQUISETINA 



Leaves in whorls and small in proportion to the stem, in the 

 form of sheaths, with long or short teeth, clasping the stem at 

 the nodes. 



The fertile branches terminate in spikes formed of leaves 

 modified in the form of peltate scales arranged in close whorls 

 with sporangia attached to their inner surface. 



Family EQUISETACE^. 



Contains the single recent genus JUguMum, and the fossil 

 species included under the generic name Equisetites. 



1 Cormack, Annals Bot. vol. vii. 1893, p. 63. 



